The instant invention relates to hydraulic seals, and specifically to a hydraulic seal for a linear actuator which is constructed to prevent extrusion of the seal material under high pressure.
Until a few years ago, maximum hydraulic operating pressures were in the 2500 PSI to 3000 PSI range. At this point in time, a 5000 PSI system is not uncommon and hydraulic systems operating at 8000 PSI are present in aircraft. System pressures are beginning to exceed the tensile strength of the materials used to seal the systems. This leads to extrusion of seal material.
One technique to prevent extrusion is known as isolation wherein the size of the extrusion gap, between the piston or rod and the cylinder, is made quite small. This requires reduced tolerances and therefore, more precise machining. Another technique to prevent extrusion is to provide a dynamic seal element having a relatively large, non-elastic edge mass.
Many forms of hydraulic seals are known. One type of seal includes a static element which includes an O-ring received in a groove on a, for example, piston, and a dynamic seal which fits over the O-ring and has a substantially cylindrical cross section. Known dynamic seals are generally formed of an elastomeric material, such as urethane. Such a dynamic seal is operable to prevent extrusion in low pressure situations, however, because such a seal is made of an elastic material to facilitate installation on a piston, the very properties which permit its installation ultimately lead to extrusion and destruction of the dynamic seal under high pressure.
Another form of dynamic seal which is known includes a split ring which allows the insertion of a dynamic seal made of a substantially non-elastic material, such as glass-filled nylon, in a hydraulic cylinder. However, under higher pressures, the presence of the split in the dynamic seal provides a leak path which allows blow-by of the hydraulic fluid, thereby lessening the operating efficiency of the hydraulic unit.
To overcome the above-mentioned problems, a dynamic seal should be formed in a continuous ring of a hard material which has high tensile strength and low elasticity. The seal should have sufficient edge mass to resist extrusion in high pressure systems, or under shock loads. The seal should be suitable for installation on a piston or rod gland without the need to stretch or compress the seal material.
An object of the instant invention is to provide a seal constructed of a resilient, substantially non-elastic material having a continuous periphery.
Another object of the instant invention is to provide a seal having sufficient edge mass to resist extrusion.
A further object of the instant invention is to provide a seal which may be installed on a piston or rod gland without stretching or compressing a dynamic seal element.
Yet another object of the instant invention is to provide a static seal having a configuration which allows easy installation of a dynamic seal thereover.
Another object of the instant invention is to provide a seal which is inexpensive to manufacture, easy to install and may be installed in existing hydraulic cylinders.